1. Field of the Invention
The present invention relates to a method and apparatus for regulating to a predetermined value the interval of seedlings to be planted in a field, such as paper-tube seedlings (i.e., soil-encased seedlings grown in soil-packed paper tubes) or plug seedlings (i.e., soil-encased seedlings grown in soil-packed plastic cells).
2. Description of the Related Art
In general, in order to increase commercial value on the market, plants such as beets and other vegetables are desired to be grown to the same or similar sizes. Therefore, when the seedlings of such plants are transplanted to a field, it is important to regulate the interval of the seedlings to a desired interval suitable for the plant; i.e., to a predetermined planting interval.
Japanese Patent Publication (kokoku) No. 7-110168 discloses a conventional seedling-interval regulation apparatus.
As shown in FIG. 16, in the conventional apparatus, two adjacent paper-tube seedlings Pn and Pn+1, among a plurality of paper-tube seedlings P, are transported successively in the vertical direction by upper transport belts 1 and 1xe2x80x2 and lower transport belts 2 and 2xe2x80x2. When a pair of seedling sensors 3 and 3xe2x80x2 detect the following paper-tube seedling Pn+1 conveyed by the upper transport belts 1 and 1xe2x80x2 after the paper-tube seedling Pn has been conveyed to the lower transport belts 2 and 2xe2x80x2, the upper transport belts 1 and 1xe2x80x2 are stopped temporarily. Subsequently, when a count value obtained from a rotary encoder 5 attached to a planting disk 4 assumes a predetermined value, rotation of the temporarily-stopped upper transport belts 1 and 1xe2x80x2 is resumed in order to maintain the interval between the two paper-tube seedlings Pn and Pn+1 at a predetermined planting interval.
The conventional apparatus is designed on the assumption that the interval t between two adjacent paper-tube seedlings Pn and Pn+1 is narrower than a predetermined planting interval. Further, the interval between two adjacent paper-tube seedlings Pn and Pn+1 is increased through temporary stoppage of the upper transport belts 1 and 1xe2x80x2, to thereby regulate their transport interval to the predetermined planting interval. Therefore, the conventional apparatus cannot cope with cases in which the paper-tube seedlings Pn and Pn+1 are conveyed at an interval greater than the predetermined planting interval.
Further, since the regulation of the transport interval t is effected through temporal stoppage of the upper transport belts 1 and 1xe2x80x2, overall processing efficiency is deteriorated.
In view of the foregoing, an object of the present invention is to provide a method and apparatus which can accurately regulate the interval of seedlings to a predetermined planting interval in both the case in which two successive seedlings are conveyed at an interval larger than the predetermined planting interval and the case in which two successive seedlings are conveyed at an interval smaller than the predetermined planting interval and which can improve overall planting efficiency.
A seedling-interval regulation method according to the present invention comprises the steps of calculating the transport interval between two adjacent seedlings successively transported by a variable speed conveyer, by measuring a distance over which the preceding seedling is transported between a point in time when the preceding seedling is detected by a seedling sensor and a point in time when the succeeding seedling is detected by the seedling sensor; comparing the calculated transport interval and a predetermined planting interval; maintaining the transport speed of the variable speed conveyer when the calculated transport interval coincides with the predetermined planting interval, and increasing or decreasing the transport speed of the variable speed conveyer or stopping the variable speed conveyer when the calculated transport interval does not coincide with the predetermined planting interval, such that the transport interval between two adjacent seedlings successively transported by the variable speed conveyer becomes equal to the predetermined planting interval immediately after the preceding seedling is discharged from the variable speed conveyer.
A seedling-interval regulation apparatus according to the present invention comprises a variable speed conveyer; seedling-interval calculation means for calculating the transport interval between two adjacent seedlings successively transported by the variable speed conveyer, by measuring a distance over which the preceding seedling is transported between a point in time when the preceding seedling is detected by a seedling sensor and a point in time when the succeeding seedling is detected by the seedling sensor; seedling-interval comparison means for comparing the calculated transport interval between the seedlings and a predetermined planting interval; and transport-speed control means for controlling the transport speed of the variable speed conveyer on the basis of the comparison result such that when the calculated transport interval coincides with the predetermined planting interval, the transport speed of the variable speed conveyer is maintained, and when the calculated transport interval does not coincide with the predetermined planting interval, the transport speed of the variable speed conveyer is increased or decreased or the variable speed conveyer is stopped, such that the transport interval between two adjacent seedlings successively transported by the variable speed conveyer becomes equal to the predetermined planting interval immediately after the preceding seedling is discharged from the variable speed conveyer.
According to the present invention, the transport interval between adjacent seedlings successively transported is regulated through an increase or decrease in the transport speed of the variable speed conveyer or through temporal stoppage of the variable speed conveyer. Accordingly, the transport interval between two adjacent seedlings successively transported can be accurately made the same as the predetermined planting interval, not only when the seedlings are transported at an interval greater than the predetermined planting interval but also when the seedlings are transported at an interval less than the predetermined planting interval.
Further, the regulation of the seedling transport interval can be performed through increasing and decreasing the transport speed of the variable speed conveyer. Therefore, overall planting efficiency can be improved.
In the present invention, the variable speed conveyer may be constituted by a pair of nipping belts, and each seedling is transported by the pair of nipping belts while being nipped between the pair of nipping belts. Alternatively, the variable speed conveyer may be constituted by a reception belt, and each seedling is transported by the reception belt while being placed on the reception belt.
In the present invention, the transport interval between two adjacent seedlings successively transported may be calculated by measuring, by use of a measuring unit, a traveling distance of the variable speed conveyer between a point in time when the preceding seedling is detected by the seedling sensor and a point in time when the succeeding seedling is detected by the seedling sensor.
In the present invention, selection of good seedlings may be performed as follows. Good and defective seedlings are transported in a horizontal orientation by a transport belt; leaf portions of only the good seedlings are nipped between a leaf-portion nipping belt and the transport belt; one of opposite side portions of the transport belt is caused to bend downward to thereby cause only the defective seedlings whose leaf portions are not nipped by the leaf-portion nipping belt to slip down to the outside of a transport path, whereby only the good seedlings are fed toward the variable speed conveyer. In this case, only good seedlings can be fed to the variable speed conveyer.
In this case, the good seedlings remaining on the transport belt without slipping down are preferably caused to come into close contact with each other. Further, a seedling feed roller may be disposed at a transport completion end of the transport belt, and the following control may be performed. When a good seedling which follows a good seedling fed to the seedling feed roller is not in close contact with the later seedling, only the traveling speed of the transport belt is increased while the rotational speed of the seedling feed roller is maintained. Thus, the transport interval of good seedlings fed to the variable speed conveyer can be made substantially constant. Accordingly, vibration in transport interval can be coped with through increasing and decreasing the seedling transport speed of the variable speed conveyer within a narrow range.
Moreover, a plurality of seedling slip-down flaps may be formed at predetermined intervals along one side portion of the transport belt. The seedling slip-down flaps bend downward upon placement of the soil-encased portions of the good and defective seedlings thereon, whereby only the defective seedlings are caused to slip down to the outside of a transport path.